In a system of networked computers, a computer communicates with other computers in the network via a data link or medium. The interface between the medium and the computer is often referred to as a network controller. The network controller interprets data from the computer and modulates an electromagnetic wave that is propagated on the medium in response to the data, and also receives and demodulates electromagnetic waves propagating on the medium in order to provide received data to the computer.
Within the context of the OSI (Open Systems Interconnection) layered communication model of the ISO (International Standards Organization), a network controller provides the function of a DLC (Data Link Control) and a PHY (Physical layer). A standard for a popular network and medium is defined in IEEE (Institute of Electrical and Electronic Engineers) standard 802.3, commonly referred to as Ethernet. Ethernet further divides the DLC so that it includes a MAC (Medium Access Control) sublayer.
In the past, a network controller usually comprised a set of semiconductor components residing on a card. However, with the number of transistors on a die increasing, the level of integration is also increasing. As a result, the MAC usually associated with a network controller may be integrated with the chipset of a personal computer. With such an arrangement, the PHY may be supplied separately by manufacturers other than the manufacturer of the chipset. Consequently, it is desirable that the interface between a MAC and PHY be flexible enough so that PHYs from different manufacturers, with possibly different numbers of pin counts and data link speeds, may be connected to the MAC. It is also desirable that the pin count for such an interface be kept as small as possible without sacrificing flexibility and future requirements.